well it just goes back to the players choice if he/she takes the risk of being Doppel, or one could also try making a non-DoV Doppel (like I did) if survivability is the problem, but trust me, it will miss a lot of potential.
which is why they reduced the def reduction on DoV as well. but 150% damage increase at level 15 is too much if it doesn’t have a drawback, doppel is our berserker kind of class that trades survivability for more attacking power. its just the way it is. I’d recommend it if you are in perma group/guild/party where someone could heal/support you but for a solo player I wouldn’t.
but like I said it’s up to the player if they are willing to risk it.
imo, they should have rather reduced the mobs stats post 280 maps instead. the def buff would make the game hell of a lot more easier now.